Rotary grinding mill short-rod and ball type



N. L. HALL March 27, 1962 ROTARY GRINDING MILL SHORT-ROD AND BALL TYPE 2 Sheets-Sheec 1 Filed Deo. 16, 1960 INVENTOR @@wmee nu lllllllllill N. L. HALL March 27, 1962 2 Sheets-Sheet 2 Filed Deo.

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Patented Mar.. 27, 1962 3,027,105 RTARY GRINDING MILL SHURT-RGD AND BALL TYPE Newton L. Hall, P1). Box 83, Salt Lake City 10, Utah Filed Dec. 16, 1960, Ser. No. 76,95 4 Claims. (Cl. 2411-184) This invention relates to horizontal rotary grinding mill and apparatus of the class described wherein the rotating and tumbling load which is carried within the mill is composed of material to be treated in combination with a grinding media of metallic or plastic parts which under rotation have grinding actions upon the material being treated to decompose, disintegrate, or alter its structural form, shape, composition or construction.

The particular application, as outlined in this specification, applies to the manufacture and use of a rotary mill with grinding media of rods, bars, or balls used for the comminution of rock products in cylindrical or conical mills, with various grinding elements. The extended ap plication of this type of mill can be used for crushing. grinding, or processing of ore or cement, other uses being the mixing, classifying, processing and finishing of chemicals, in a tube mili or kiln, and the aggiomerating and pelletizing of granular substances for an extension of processing treatment. The horizontal cylindrical and conical mills have a wide application in the industries due to their practical shape, low up-keep, efliciency of operation, and high capacity.

Ball mills are so termed in the trade when using balls as a grinding media in the mill load; rod mills when using rods or bars, and tube mills when using balls in mills of several diameters in length of cylinder, the term tube referring to the tubular cylinder forming the mill structure, regardless of the type of grinding media being used. Conical mills refer to mills of coniform, i.e. cone-shaped, form of the mill structure with a coned feed section based on an interposed cylindrical grinding section supporting a coned classifying section based in reversed position at the opposite discharge end of the cylindrical section, the three sections being in single alinement and of clear interior forming a conical mill shell. ln the following descriptions the trade name and terms will be used and applied to ball, rod, tube, or conical mills. The rod or bar used as a grinding unit will be termed rod and the rod of mill cylinder length as a long rod, and of less than diametral length of mill cylinder as a short rod.

Ball mills are commonly used for fine grinding and produce a product of over 20() mesh per square inch in screen size. Large balls of 4 or 5 inches in diameter are used for crushing in mills approximating l feet in diameter, and balls of less than 2 inches in diameter are used for fine grinding, The Weight of steel balls will average 300 pounds per cubic foot and with pulp illing the voids between the balls, will increase the weight to 400 pounds per cubic foot. Grinding mill will average from to 14 feet or more in diameter with ball mills of two diameters and tube mills of several diameters in length. Mills operate on wet or dry grinding and tube mills operate on line grinding and processing under heat.

The common type of power applied for operation of rotary mills is the conventional i.e. customary type of geared motor drive. For ore reduction, the mine run of ore is reduced in mills of the gyratory or jaw types and pass the broken ore over a coarse screen. termed a grizzley or grate, and in turn deliver the under-size to a primary roll or disc Crusher, and then to a primary ball mill of large diameter using large balls and in turn delivering the product to secondary ball mills using small ball for extreme tine grinding. Rod mills are being'substituted for the rolls, making a product suitable for the primary ball mills. Rod mills are of the same construc tion as ball mills and use steel rods or bars of substantially the interior length of the mill for a grinding media. Rods are of diameters up to 4 inches and a mill load of rods may fill the mill almost to half the volumetric mill capacity.

In a cylindrical mill, the rods are in axial alinement to the mill cylinder whereas the rotative action of the mill and load is in normal alinement to the mill axis. One of the distinguishing features outlined in the following specifications concerns the length of rod used in the mill, that length being less than the mill clear diameter, the short length preventing the rod binding across the mill diameter and allowing the rod to rotate lengthwise, end for end, in a radial plane which is normal to the vmill axis, contrary to the action of long rods of cylindrical length, which are confined to a rolling radial action.

The mill load has actions when under rotation which are erratic and can not easily be determined by the mill operator.

The amount and condition of the ore forming the mill load may vary, become hard or soft, gritty or slimy, and the conditions of the load at each end of the grinding rod and mill may vary, gripping the long rod at one end and liberating it at the other end, developing actions in the rod to the extent that the rods will be out of alinement with and disturb the adjoining rods resulting in a pell-mell violence which accounts for the crude product andthe difference of screen sizing as produced by mills grinding a stabilized mill load. g

One of the objects of this invention is to place the grinding and mill load elements in a coniform rotarymill for rotation with the mill and load radial movements and with the short rods in lengthwise overturning,`.'end over end of rod movement in line Vwith the radial plane of mill and load rotation with the discharge cone head effecting a classification, withdrawal and dischargeof ground product from the mill through the discharge trunnion and from the mill.

Another object is to place short rods in the load to take a radial position and in action to rotate in overturning lengthwise, with the short rod in conformity to the planes of radial rotation of the load, serving to break the compact solidarity of the load near the load heart and increase the mill load action within the body ofthe load.

Another object is to provide the short grinding rods of a length whereby they can command and control the depth of active load and retain the radial position of rods, or rods and balls, within the load without undue contact with the mill lining or mill shell, cushioning the rods from striking the mill clear or exposed interior from rod action.

Another object is to use a conical mill with central uniform section and coniform feed and discharge sections, whereby the oversize of the mill load is retained Within the central section of uniform diameter and the undersize are classilied to each coniform section, the discharge section having a classified product of undersize for withdrawal and discharge.

Another object is to use conical mill cylinders with coniform end walls to elfect a return movement to vagrant short rods which have taken an axial alinement position within the load, thereby allowing the displaced short rod to automatically regain its radial position with adjacent rods and reenter the mill load in positions of radial mill load planes.

One of the objects of this invention is to combine the short rod and the ball as a grinding medium in a conical mill to substitute the rod cylindrical mill of uniform diameter, the substitution being to use a conical mill as a rod mill, or as a combined rod and ball mill, placing the short rods within the mill with the rods being of less than diametral length whereby the rods will freely take a position within the load and act in a plane which is normal to the mill axis, a position contrary to the position taken by the mill length of long rod of the conventional rod mill of uniform diameter which has the long rods acting practically parallel to the mill axis and out of alinment with the direction of load and radial mill rotation, and out of alinement with adjoining rods of the load, substituting the rolling circular motion of the long rod with the end over end lengthwise overturning of the short rod, supplanting the rolling contact action of adjoining rods with an action of breaking up the compact mill load and placing a movement within the consolidated mill load for extended action.

Another object is to reduce the number and extent of steel rods required by placing the mill action within the load movement versus the pell-mell process in use with long rods engaging with a rolling circular contact grinding.

Another object is to use a conical mill with central section of uniform diameter and coniform feed and discharge sections whereby the over size of the mill load is retained within the central uniform section and the undersize are classified to each respective coniform section, the discharge section having a classified product of undersize for withdrawal and discharge.

Other objectives may become apparent as the invention is disclosed.

In the drawings:

FIGURE 1 represents a vertical and longitudinal section of a conical ball mill of short length with mill load of steel short rods and balls taken on line 1 1 of FIG- URE 3.

FIGURE 2 represents a cross section of a conical mill, similar to FIG. 3 of steel balls only without short grinding rods, the load being under action in comparison to the mill load shown in FIG. 3.

FIGURE 3 represents a cross section of a mill cylinder with mill load under action, the section being taken on line 3-3 of FIG. 1.

FIGURE 4 represents a vertical and longitudinal section of a conical ball mill of long length with mill based upon an inclinable frame support with the cylindrical mill section being similar to FIG. 1.

FIGURE 5 is a lateral view of a single short grinding rod with enlarged terminals, as shown in FIG. 4.

FIGURE 6 is a lateral view, similar to FIG. 5 with enlarged collar on the rod midway between the rod and terminals.

In the drawings:

Referring to FIGURE 1; the conical mill cylinder is noted by the numeral l-a for the middle section of uniform diameter, as 1-b for the conical head section, and as 1-c for the conical classifying and discharge head section, the three sections comprising the conical mill cylinder. The conical mill rotates in the bearings 2-a at the feed head and Z-b at the discharge head. The conical feed head is supported by the hollow feed trunnion bearing 3-a and the conical classifying and open discharge trunnion bearing 3-b. The mill rests upon the abutments 4-a at the feed head and 4-b at the discharge head. The mill is operated by the main gear S-a, driven by the drive pinion S-b, FIG. 3, and in turn operated by the drive shaft S-c from any customary source of electrical power.

The sections of the mill cylinder are lined with wear protective liner plates 6-a formed of alloyed or hardened steel.

The mill receives its load from the feed scoop 7-a, with its central removable center piece 7-b.

The various mill features which adjoin are suitably attached by rivet, bolt, or weld.

The mill load of FIGS. l and 3 are composed of steel balls and short rods, that is, rods of length less than the mill diameter. Ball diameters wear in service and vary in radial measurements from ve inches. The maximum diameter of rods preferably do not exceed the radial dimension of new balls, the general average ranging from four inches or less.

FIGURE 4 has the mill section of uniform diameter and length extended to an approximate measurement equal to two mill diameters with the conical discharge head terminating in a removable grating cone S, extending out-side of the conical head proper with attaching bolts S-a and supplanting the mill manhole, the conical head being supported by the roller bearing 2-c. At the conical feed head the hollow trunnion friction bearing is noted as La. The conical feed head and trunnion bearing is fed from the feed scoop 7-a provided with a central removable center piece 7-b which upon rem-oval allows a limited direct entry along the trunnion axis and towards the mill interior.

The entire conical mill structure is supported upon the inclinable A frame 9 which in turn is balanced over the dual fulcrums 110, one at each end of the cross member of the A with the control of the inclination being governed by the single hydraulic lifting jack 10-a which is further controlled by the dual compression springs 10-b at the spread terminals of the A frame, allowing a limited change of slope to the mill axis to provide for the mill load control and discharge of the classified load. The ball mill load is noted at 11-a towards the conical feeding section of the mill, and as 11-b towards the conical classifying and discharge section.

The drive gear 5-a is similar to the drive arrangement as noted in FIGS. 1 and 3. The short rod grinding bar 12 is shown in grinding position in the load. In FIGS. l and 3 the short rod is shown of one uniform diametral measurement along its length. In FIG. 4, the short rod shown 4in the load with the rod mid-section of smaller or less radial diameter 12-a and with the rod ends or terminals of enlarged diameter, l12-a.

The mill load of a conical mill is preferably maintained at a level which is of a volume close to fifty percent of the volumetric mill capacity. The characteristics of the coniform mill section in discharge thtrough the outlet trunnion can be altered by a slight change in the axial slope and inclination of the mill developing a change in the natural conical classification of the mill product.

Similar numerals refer to similar parts in all of the views.

In its Operation the short-rod and ball conical mill has objectives to develop a mill load of complete activity as noted in FIG. 2 vs. FIG. 3, wherein the short rod, acting within the plane of load rotation, breaks into the quiescent heart H of the mill load and stirs the comparatively quiet load into action twice for each lengthwise end over end rotation of the short rod moving within the radial plane of load rotation, that is, a movement which is normal to the mill axis. Rods of rod mill loads which are of length greater than the mill diameter necessarily must take an axial position and w-ith the mill rotation must rotate and roll sideways to their length, and, as with the conventional rod mill, must tumble over the load cascade' to reach the load toe, will crush load material in position between the longitudinally or parallel and adjacent rods.

In comparison to this related action, the short rod in lengthwise rotation will extend from the load with one end, or rod terminal, free and outside of the load and above the load cascade surface, and in descending will cause the exposed terminal to descend and strike the load toe at T with a decided impact, an action which is absent and not found in the conventional rod mill. lIn no case does the conventional rod mill action take a lengthwise end over end radial action.

Vagrant short rods which tend to take an axial alinement position, can reach the mill cone and with the end of the rod bearing against the rising side of the cone shell, may be forced and lifted towards the load radial position and automatically resume a radial alinement which is in line with the other short rods of the mill load.

The short rod has a length which is less than the neat clear diameter of the mill. When rotating end over end the short rod should have a length whereby the descending rod terminal reaches the load toe, a suiiicient amount of toe load material should be formed to provide a load cushion to the descending terminal of the rod, and to provide a collection of load between the rod and the shell to cushion the rod terminal in its crushing action and to avoid undue action upon the mill linings.

The radial spacing of the short rods in a straight axial alinement should preferably be, one half of the number of rods for the axial distance covered, that is, a rod with an original terminal (l2-d) width of tive inches should be placed on a ten inch center spacing; accordingly, a single axial row of short rods which can automatically take an axial alinement while in a radial position to form a single row of short rods, can provide a collective load action comparable as example, to the action of a load of long rods which are placed axially within the mill to a depth of 40 to 50` percent of the mill capacity, such rods acting in a radial rolling and cascading motion in line with the diametral or radial plane.

Under such comparative examples, the long rods are taking position within the load that could be provided for the mill load, aside from the required grinding ball media.

The long rod acts with a rolling motion to cascade over the mill load. The short rod of this invention acts with a longitudinal sweep bringing approximately one half of the rod against the load toe in impact action, the em beded end of the rod reacting to break a consolidated packing of the load which is within its rising terminal portion.

The number of short rods required should be limited to avoid a bunching or grouping of rods collectively. Continued mill operation can serve to spread the rods into axial alinement with the rods in diametral and spaced arrangement. In point of steel cost for rods, the total steel required for comparative examples is a considerable economy favoring the short rods. Short rods can be handled and transported at a low cost. Too many rods in the load will defeat the proper and natural spacing. The conventional rod mill has a rod load with rods positioned longitudinally in axial alinement vs. the short bar and ball mill which has the rods spaced on centers which allow an open space between adjacent rods with mill loadballs and pulp-intervening As shown in FIGS. 5 and 6, the middle portion of the rod length l2-a can be reduced in diameter, considerably reducing the amount of special steel required to meet the crushing rod requirements. The reduced mid-sections provide a temporary anchorage for the short rod to maintain a central position within the mill load and avoid a striking of the descending rod terminal 12a against the mill shell or lining. The mid-section enlargement, 12-b of FIG. 6, can be formed of a rubber sleeve attached to the rod mid-section and serve as additional anchorage of the rod in maintaining a central position Within the rotating mill load.

The conventional motive power mechanism operating the drive shaft S-c is suitably mounted upon the A frame 9 providing an allowance for the driving mechanism and equipment to be inclined or tilted as a unit and with the mill.

The natural classication of the mill load as developed over the rotating conical section of mill shell is sensitive to the inclination provided to the mill axis and only a slight alter-ation of slope will mark a chang-e in the sizing of load at the apex of the cone for mill product discharge.

The Yarrow points R in the views note the direction of mill rotations and in FIGS. l and 4 as extended `from the further side of Ithe mill cylinder and towards the near side of the views.

ln the claims:

l. A horizontal rotary cylindrical grinding mill of clear interior and imperforate shell, open at both ends for respectively receiving and discharging a circulating load of material to be ground, said mill containing a load with grinding elements of short grinding rods of less length than the clear diametral width of said mill interior, said rods being adapted to singly and independently rotate lengthwise end over end in radial planes of said load and in direction normal to said mill axis, said load being adapted to operate under normal mill and load speed and actions.

2. A horizontal rotary cylindrical grinding mill of clear interior and imperforate shell open at both ends for respectively receiving and discharging a circulating load of discrete material to be ground, comprising;

a rotatable mill cylinder of uniform shell diameter adapted to contain and engage a rotatable load of discrete material combined with grinding elements of short rods and balls said rods and balls being of similar conventional diameters said rods being of less length than said mill clear interior diameter and combined with said ball load to independently operate in radial lengthwise end over end rotation within and with said mill road under normal rotation of speed of said mill and load action.

3. A horizontal rotary grinding mill of the conical mill type of clear interior, and imperforate shell open at both ends for respectively receiving and discharging a circulating load of material to be ground, comprising;

a rotatable mill cylinder of sections in single axial alinemen-t with grinding section of uniform shell diameter intervening and attached to a feed section of coniform mill head and an opposite classifying and discharge section of conform mill head, said combination of sections comprising a single compar-tment conical mill adapted to contain and engage a rotatable load of circulating discrete material with grinding elements of steel short rods and balls, the width of said rods being similar to said grinding ball conventional diameter and of length less than said mill clear interior diameter and -free and independA ent to operate Isingly or collectively within and with said mill load in lengthwise end over end radial ro* tation under normal radial rotation of said mill and load action, said conform mill and discharge section serving lto classify and segregate said load and pass undersize in discharge from said section and mill.

4. A horizontal rotary grinding mill of the conical mill type of clear interior and imperforate shell open at both ends for respectively receiving and discharging a circulating load of material to be ground, compri-sing;

a rotatable mill cylinder of sections in single axial alinement with grinding section of uniform shell diameter intervening and attached to a section of coniform mill feed head and an opposite coniform classifying and discharge mill head, said sections comprising a conical mill of `single clear interior and alinement, based upon an inclinable frame support and said mill being adapted to contain and engage a rotatable load of circulating discrete material with grinding elements of short rods and balls, the diametral width of said rods being similar to s-aid ball conventional diameter and of length less than said mill clear interior diameter and free and independent to operate singly, or collectively in lengthwise end over end radial rotation within and with said load under normal radial rotation of said mill and load action, said coniform mill end discharge section serving to classify and segregate said load and pass undersiz in discharge from said section and mill.

References Cied in the le of this patent UNITED STATES PATENTS 

